Observations on the oestrous cycle of the Friesian heifer
Wishart, D.F.
Veterinary Record 90(21): 595-597
1972
ISSN/ISBN: 0042-4900 PMID: 4672455 Document Number: 55140
Between Mar. 1970 and May 1971, observations of 211 oestrous cycles were recorded. Average cycle length during spring-summer was 20-02 +or-4-6 days nu 26-17 +or- 0-8 in autumn-winter. Within-heifer variation in cycle length was < 2 days in 77-3% of cycles, but could be as much as 5 days in some cases. Of 127 observed over four 5- to 7-day periods, 66 exhibited oestrus. The mean duration of oestrus was 14-7 +or-1-6 hr.